The present invention relates to wireless communication apparatuses and wireless communication methods, and more particularly, to an AP (access point: wireless base station) and an interference control method that are suitable for uplink communications from MS's (mobile stations) to the AP in the case where the communications are performed between plural MS's and the AP at the same frequency and at the same time with the use of space division multiple access.
In recent years, as the field of communication antennas has been developing, a MIMO (multi-input multi-output) communication method that performs communication using plural antennas has become widely used. In the MIMO system, communication capacity can be increased by maximizing the number of channels between transmitters and receivers with the use of the maximum number of antennas. In addition, if technologies used in the MIMO communication method are seen from another point of view, this method can be said to include the following two technologies.
(1) SDMA (space division multiple access) technology that makes it possible for an AP to communicate with different MS's.
(2) SDM (space division multiplexing) technology that makes it possible for an AP to communicate with the same MS.
The SDMA technology is a technology in which different weighted coefficients (weights) are used for plural antennas respectively so that the magnitudes and phases of signals transmitted and received through the antennas can be adjusted, and different data series can be transmitted to plural MS's at the same frequency and at the same time by using spatial orthogonality in a propagation path. On the other hand, the SDM technology is a technology in which different weighted coefficients (weights) are used for plural antennas respectively so that the magnitudes and phases of signals transmitted and received through the antennas can be adjusted, and different data series can be transmitted to the same MS at the same frequency and at the same time by using spatial orthogonality in a propagation path.
In addition, there is a MIMO-SDMA technology created by combining these SDMA and SDM technologies. This technology is a technology in which the SDMA (space division multiple access) is used for data transmission to different MS's, and the SDM (space division multiplexing) is used for data transmission to the same MS, and this technology is also referred to as MU-MIMO (multi-user MIMO). The MU-MIMO technology is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2008-211349. In addition, the SDMA technology is disclosed, for example, in T. Ohgane, “A Study on a Channel Allocation Scheme with an Adaptive Array in SDMA,” IEEE 47th VTC, Vol. 2, 1997, pp. 725-729. The SDM technology is disclosed, for example, in G. J. Foschini, “Layered Space-Time Architecture for Wireless Communication in Fading Environment When Using Multi-Element Antennas,” Bell Labs Tech. J, autumn 1996, pp. 41-59. In addition, the MIMO-SDMA technology is disclosed in Andre Bourdoux, Nadia Khaled, “Joint TX-RX Optimization for MIMO-SDMA Based on a Null-space Constraint,” IEEE 2002, pp. 171-174. In addition, a technology in which wireless resources are distributed to SDMA groups on the basis of propagation qualities and required communication qualities.